By way of definition a progressive slide assembly, sometimes referred to in the art as a progressive slide suspension, is known in the trade as one wherein the two moving slides of the three slide assembly move outwardly progressively so that both slides reach full travel simultaneously; as opposed to the older type of assembly wherein one slide moves outwardly, collects the second slide and pulls the latter out to its full extension. It is recognized that progressive slide assemblies have several advantages in that they are normally quieter in operation, are smoother acting, distribute the load more evenly and remain operable over longer periods of use.
Progressive slide assemblies are used extensively, but not exclusively, for slidingly supporting the drawers of filing cabinets and are characterized generally by three channel shaped members arranged in nested relationship, one slide, hereinafter referred to as the outer slide, being secured to the file cabinet and the other two slides, that is the intermediate and inner slides, being slidable longitudinally relative to the fixed outer slide and to each other, the inner slide being the one which supports the filing cabinet drawer. In the past it has been the practice to provide progressive slide action between the intermediate and outer slides by means of one or more anti-friction elements, that is to say ball bearings, sometimes referred to as propeller ball(s). Typical of these earlier progressive slide assemblies are the drawer suspensions shown in U.S. Pat. No. 1,963,220 Anderson 6/19/34, U.S. Pat. No. 2,346,167 Jones et al. 4/11/44 and U.S. Pat. No. 2,805,106 Penkala 9/3/57. In the aforesaid patents the progressive action of the slides is effected by a propeller ball and hence is not a positive drive between the moving slides but is dependent on friction drive which, in turn, is dependent on continuity of the applied load, that is to say, if the load on the slides is insufficient the friction drive of the propeller ball fails and the progressive action of the slides is cancelled out.
Other known designs use a wheel as the friction drive; and U.S. Pat. No. 3,545,833 Stein 12/8/70 describes a progressive slide assembly alleged to overcome the disadvantages of friction drive by utilizing a flexible cable arranged in the form of a loop with its ends secured to the outer slide, the cable being looped over suitably spaced pullies or pins projecting from the intermediate slide. While this design may avoid dependency on load for effecting progressive action of the slides it is nevertheless dependent on friction drive and hence is less than positive.